diff --git a/mock/mock.go b/mock/mock.go
index 114fca619..efc89deff 100644
--- a/mock/mock.go
+++ b/mock/mock.go
@@ -948,8 +948,6 @@ func (args Arguments) Is(objects ...interface{}) bool {
 	return true
 }
 
-type outputRenderer func() string
-
 // Diff gets a string describing the differences between the arguments
 // and the specified objects.
 //
@@ -957,7 +955,7 @@ type outputRenderer func() string
 func (args Arguments) Diff(objects []interface{}) (string, int) {
 	// TODO: could return string as error and nil for No difference
 
-	var outputBuilder strings.Builder
+	output := "\n"
 	var differences int
 
 	maxArgCount := len(args)
@@ -965,35 +963,24 @@ func (args Arguments) Diff(objects []interface{}) (string, int) {
 		maxArgCount = len(objects)
 	}
 
-	outputRenderers := []outputRenderer{}
-
 	for i := 0; i < maxArgCount; i++ {
-		i := i
 		var actual, expected interface{}
-		var actualFmt, expectedFmt func() string
+		var actualFmt, expectedFmt string
 
 		if len(objects) <= i {
 			actual = "(Missing)"
-			actualFmt = func() string {
-				return "(Missing)"
-			}
+			actualFmt = "(Missing)"
 		} else {
 			actual = objects[i]
-			actualFmt = func() string {
-				return fmt.Sprintf("(%[1]T=%[1]v)", actual)
-			}
+			actualFmt = fmt.Sprintf("(%[1]T=%[1]v)", actual)
 		}
 
 		if len(args) <= i {
 			expected = "(Missing)"
-			expectedFmt = func() string {
-				return "(Missing)"
-			}
+			expectedFmt = "(Missing)"
 		} else {
 			expected = args[i]
-			expectedFmt = func() string {
-				return fmt.Sprintf("(%[1]T=%[1]v)", expected)
-			}
+			expectedFmt = fmt.Sprintf("(%[1]T=%[1]v)", expected)
 		}
 
 		if matcher, ok := expected.(argumentMatcher); ok {
@@ -1001,22 +988,16 @@ func (args Arguments) Diff(objects []interface{}) (string, int) {
 			func() {
 				defer func() {
 					if r := recover(); r != nil {
-						actualFmt = func() string {
-							return fmt.Sprintf("panic in argument matcher: %v", r)
-						}
+						actualFmt = fmt.Sprintf("panic in argument matcher: %v", r)
 					}
 				}()
 				matches = matcher.Matches(actual)
 			}()
 			if matches {
-				outputRenderers = append(outputRenderers, func() string {
-					return fmt.Sprintf("\t%d: PASS:  %s matched by %s\n", i, actualFmt(), matcher)
-				})
+				output = fmt.Sprintf("%s\t%d: PASS:  %s matched by %s\n", output, i, actualFmt, matcher)
 			} else {
 				differences++
-				outputRenderers = append(outputRenderers, func() string {
-					return fmt.Sprintf("\t%d: FAIL:  %s not matched by %s\n", i, actualFmt(), matcher)
-				})
+				output = fmt.Sprintf("%s\t%d: FAIL:  %s not matched by %s\n", output, i, actualFmt, matcher)
 			}
 		} else {
 			switch expected := expected.(type) {
@@ -1025,17 +1006,13 @@ func (args Arguments) Diff(objects []interface{}) (string, int) {
 				if reflect.TypeOf(actual).Name() != string(expected) && reflect.TypeOf(actual).String() != string(expected) {
 					// not match
 					differences++
-					outputRenderers = append(outputRenderers, func() string {
-						return fmt.Sprintf("\t%d: FAIL:  type %s != type %s - %s\n", i, expected, reflect.TypeOf(actual).Name(), actualFmt())
-					})
+					output = fmt.Sprintf("%s\t%d: FAIL:  type %s != type %s - %s\n", output, i, expected, reflect.TypeOf(actual).Name(), actualFmt)
 				}
 			case *IsTypeArgument:
 				actualT := reflect.TypeOf(actual)
 				if actualT != expected.t {
 					differences++
-					outputRenderers = append(outputRenderers, func() string {
-						return fmt.Sprintf("\t%d: FAIL:  type %s != type %s - %s\n", i, expected.t.Name(), actualT.Name(), actualFmt())
-					})
+					output = fmt.Sprintf("%s\t%d: FAIL:  type %s != type %s - %s\n", output, i, expected.t.Name(), actualT.Name(), actualFmt)
 				}
 			case *FunctionalOptionsArgument:
 				var name string
@@ -1046,36 +1023,26 @@ func (args Arguments) Diff(objects []interface{}) (string, int) {
 				const tName = "[]interface{}"
 				if name != reflect.TypeOf(actual).String() && len(expected.values) != 0 {
 					differences++
-					outputRenderers = append(outputRenderers, func() string {
-						return fmt.Sprintf("\t%d: FAIL:  type %s != type %s - %s\n", i, tName, reflect.TypeOf(actual).Name(), actualFmt())
-					})
+					output = fmt.Sprintf("%s\t%d: FAIL:  type %s != type %s - %s\n", output, i, tName, reflect.TypeOf(actual).Name(), actualFmt)
 				} else {
 					if ef, af := assertOpts(expected.values, actual); ef == "" && af == "" {
 						// match
-						outputRenderers = append(outputRenderers, func() string {
-							return fmt.Sprintf("\t%d: PASS:  %s == %s\n", i, tName, tName)
-						})
+						output = fmt.Sprintf("%s\t%d: PASS:  %s == %s\n", output, i, tName, tName)
 					} else {
 						// not match
 						differences++
-						outputRenderers = append(outputRenderers, func() string {
-							return fmt.Sprintf("\t%d: FAIL:  %s != %s\n", i, af, ef)
-						})
+						output = fmt.Sprintf("%s\t%d: FAIL:  %s != %s\n", output, i, af, ef)
 					}
 				}
 
 			default:
 				if assert.ObjectsAreEqual(expected, Anything) || assert.ObjectsAreEqual(actual, Anything) || assert.ObjectsAreEqual(actual, expected) {
 					// match
-					outputRenderers = append(outputRenderers, func() string {
-						return fmt.Sprintf("\t%d: PASS:  %s == %s\n", i, actualFmt(), expectedFmt())
-					})
+					output = fmt.Sprintf("%s\t%d: PASS:  %s == %s\n", output, i, actualFmt, expectedFmt)
 				} else {
 					// not match
 					differences++
-					outputRenderers = append(outputRenderers, func() string {
-						return fmt.Sprintf("\t%d: FAIL:  %s != %s\n", i, actualFmt(), expectedFmt())
-					})
+					output = fmt.Sprintf("%s\t%d: FAIL:  %s != %s\n", output, i, actualFmt, expectedFmt)
 				}
 			}
 		}
@@ -1086,12 +1053,7 @@ func (args Arguments) Diff(objects []interface{}) (string, int) {
 		return "No differences.", differences
 	}
 
-	outputBuilder.WriteString("\n")
-	for _, r := range outputRenderers {
-		outputBuilder.WriteString(r())
-	}
-
-	return outputBuilder.String(), differences
+	return output, differences
 }
 
 // Assert compares the arguments with the specified objects and fails if
diff --git a/mock/mock_test.go b/mock/mock_test.go
index 813ec5e56..eafc9fb1a 100644
--- a/mock/mock_test.go
+++ b/mock/mock_test.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"regexp"
 	"runtime"
+	"strconv"
 	"sync"
 	"testing"
 	"time"
@@ -2421,3 +2422,22 @@ type user interface {
 type mockUser struct{ Mock }
 
 func (m *mockUser) Use(c caller) { m.Called(c) }
+
+type mutatingStringer struct {
+	N int
+	s string
+}
+
+func (m *mutatingStringer) String() string {
+	m.s = strconv.Itoa(m.N)
+	return m.s
+}
+
+func TestIssue1785ArgumentWithMutatingStringer(t *testing.T) {
+	m := &Mock{}
+	m.On("Method", &mutatingStringer{N: 2})
+	m.On("Method", &mutatingStringer{N: 1})
+	m.MethodCalled("Method", &mutatingStringer{N: 1})
+	m.MethodCalled("Method", &mutatingStringer{N: 2})
+	m.AssertExpectations(t)
+}